The present invention relates to a discharge elbow provided with guide vanes to be disposed in a pipeline, a duct, etc.
Expansion ducts for rectifying and decelerating fluid flow include diffusers (straight ducts), expansion elbows (right angled bent ducts), etc.
The technical characteristics of the diffuser have been elucidated. A diffuser pump wherein diffuser guide vanes are disposed around an impeller is the most popular example of the application of the diffuser. The diffuser pump has an advantage in that the guide vanes effectively decelerate high-speed liquid discharging from the impeller to convert high velocity head to pressure head. Therefore, the diffuser pump has the advantage of restoring hydrostatic pressure, thereby increasing pump head. Another popular example of the application of the diffuser is a diffuser duct used in a wind tunnel. The diffuser duct decelerates high-speed airflow discharging from a blower to restore hydrostatic pressure.
However, development of rectification technology by an expansion elbow has not been achieved though it has been strongly desired. In order to solve this problem, the inventor of the present invention proposed a discharge elbow provided with guide vanes in the patent document No. 1.    Patent document No. 1: Japanese Patent No. 2706222 (U.S. Pat. No. 5,531,484)
The discharge elbow provided with guide vanes of the patent document No. 1 comprises an elbow of rectangular cross section and magnification f of 1<f≦5, and one or more guide vanes disposed in the elbow, while the guide vane or the guide vanes are made of a curved plate and a pair of flat plates connected to the curved plate, with one of them being located in front of the curved plate and the other being located to the rear of the curved plate, wherein the inner sidewall of the elbow, the outer sidewall of the elbow and the guide vane or the guide vanes cooperate to define m number of sub-channels similar to one another based on the following formulas.p=h/{[f/(f−r)]m−1}  (1)an=pr[f/(f−r)]n  (2)bn=an/f  (3)p: overhang length at the outlet of the elbowh: inlet breadth of the elbowW: outlet breadth of the elbowf: magnification of the elbow (f=W/h)r: aspect ratio of the sub-channels (r<f)m: number of sub-channels (m≧2)an: outlet breadth of n-th sub-channel (a0 indicates the radius of curvature of the inner sidewall and am indicates the radius of curvature of the outer sidewall)bn: inlet breadth of n-th sub-channel
FIG. 1 shows an expansion elbow 1, which is an example of the discharge elbow provided with guide vanes of the patent document No. 1.
In the expansion elbow 1, guide vanes 5, 6 and 7 are right angled curved guide plates each of them being made of a quarter circular curved plate and a pair of flat plates connected to the curved plate, with one of them being located in front of the curved plate and the other being located to the rear of the curved plate.
In FIG. 1, the aspect ratio r of the sub-channels means A1C1/A1A2, A2C2/A2A3, A3C3/A3A4 . . . in rectangles A1C1B2A2, A2C2B3A3, A3C3B4A4 . . . . .
The discharge elbow of the patent document No. 1 achieves a discharge of uniform parallel flow, wherein velocity distribution is uniform and flow direction is concentrated in one direction by disposing one or more guide vanes in the elbow to make a plurality of sub-channels similar to one another.
The discharge elbow provided with guide vanes of the patent document No. 1 can be used for any one of a reduction elbow (magnification f: f<1), a normal elbow (magnification f: f=1), or an expansion elbow (magnification f: 1<f≦25). Of particular note is that the expansion discharge elbow provided with guide vanes has good potential in various fields.
The discharge elbow provided with guide vanes of the patent document No. 1 has a problem in that a separation vortex survives in n=1 sub-channel along the inner sidewall of the elbow to stagnate the flow there. Therefore, partial absence of air curtain, partial accumulation of dust, etc. may occur when the discharge elbow provided with guide vanes of the patent document No. 1 is used in an air curtain, a heat exchanger, etc.
The flow line of the discharge elbow provided with guide vanes of FIG. 1 is shown in FIG. 2. Fluid enters into the expansion elbow 1 through the inlet 2 of the elbow to separately enter into four sub-channels formed by the inner sidewall 4, the guide vanes 5, 6 and 7 and the outer sidewall 8, thereby being decelerated. Separation vortices, each thereof being formed by a plurality of small vortices, are generated along the convex rear surfaces of the inner sidewall 4 and the guide vanes 5, 6 and 7 to stagnate at the location of the outlet 3 of the elbow. High-speed fluid flowing along the concave front surfaces of the guide vanes 5, 6 and 7 contacts and attracts the separation vortices generated along the convex rear surfaces of the guide vanes 5, 6 and 7 at the location of the outlet 3 of the elbow to form a fixed single vortex 10 in n=2 sub-channel, a fixed single vortex 11 in n=3 sub-channel and a fixed single vortex 12 in n=4 sub-channel at the location of the outlet 3 of the elbow. The sizes of the fixed single vortex 10, the fixed single vortex 11 and the fixed single vortex 12 are in proportion to the sizes of the sub-channels. The centers of the fixed single vortex 10, the fixed single vortex 11 and the fixed single vortex 12 are aligned on a straight line formed by the outlet 3 of the elbow and extending at right angles to the discharge direction of the elbow. Regarding the phenomenon of a separation vortex being changed into a fixed single vortex by the attraction of high-speed flow of fluid, a paper titled “Numerical Analysis of Wind Concentration around Wind Turbines Shrouded by Brimmed Diffuser” (Collection of papers read at a symposium on computational fluid dynamics, Kyushu University, Masato FURUYA, et al. 2003) reports a method for increasing flow rate of discharge air from a generator wind turbine, wherein the generator wind turbine is provided with a diffuser shroud, and a separation vortex formed inside the shroud is attracted by high-speed external air flow to be changed into a fixed single vortex, thereby increasing flow rate.
In the n=2 sub-channel, n=3 sub-channel and n=4 sub channel, flows adjacent the fixed single vortex 10, the fixed single vortex 11 and the fixed single vortex 12 go around them to be decelerated and enlarged without being contracted, thereby becoming uniform parallel flows.
However, in the n=1 sub-channel, a separation vortex 9 generated along the convex rear surface of the inner sidewall 4 of the elbow survives without being changed into a fixed single vortex because of the absence of an adjacent high-speed flow of the fluid to expand along a duct wall extending downstream of the inner sidewall of the elbow beyond the outlet 3 of the elbow. The separation vortex contracts and disappears as the distance from the outlet 3 of the elbow increases.
FIG. 3 shows the velocity distribution of the fluid corresponding to the flow line of FIG. 2. The centers of the fixed single vortex 10, the fixed single vortex 11 and the fixed single vortex 12 and the separation vortex 9 lie at the location X0 coinciding with the location of the outlet 3 of the elbow. At the location X1 downstream of the regions of the fixed single vortex 10, the fixed single vortex 11 and the fixed single vortex 12, high-speed flows with the same velocity along the concave front surfaces of the guide vanes 5, 6 and 7 coexist with decelerated flows formed by the flows going around the fixed single vortex 10, the fixed single vortex 11 and the fixed single vortex 12 to be enlarged to form a wave-shaped velocity distribution. The high-speed flow along the concave front surface of the outer sidewall 8 of the elbow becomes a flow along a wall to be scarcely decelerated. The separation vortex 9 along the convex rear surface of the inner sidewall 4 of the elbow survives to form a reverse flow along a duct wall downstream of the inner sidewall of the elbow. At the location X2 downstream of the location X1, the velocity distribution becomes uniform and parallel except in the region close to the duct wall downstream of the inner sidewall of the elbow. However, the reverse flow survives along the duct wall downstream of the inner sidewall of the elbow. The reverse flow damps as the distance from the outlet 3 of the elbow increases.
FIG. 4 shows a decelerated jet flow blowing out of a discharge elbow provided with guide vanes with magnification f being equal to 5 when a high-speed airflow with the velocity of 12 m/sec. flows into the elbow. Each fixed single vortex formed at the location of the outlet 3 of the elbow shown in FIG. 3 is made visible as each transparent portion. The each fixed single vortex is made visible for a very short time less than one second just after white smoke is put into the airflow and just before the each fixed single vortex is filled with the white smoke and made invisible after the each single fixed vortex is filled with white smoke. It can be seen from FIG. 4 that the decelerated jet flow shown in FIG. 4 is generally in a form of rectangle in good order and lines of the flows of the discharge air are concentrated in the same direction. No white smoke can be seen in the left end portion of the outlet 3 of the discharge elbow corresponding to the n=1 sub-channel because of the reverse flow. Therefore, when the elbow is used independently for blowing out a jet flow, the n=1 sub-channel does not operate as an outlet of the elbow. In either the case where the elbow is used independently for blowing out a jet flow or the case where the elbow is used in a duct, absence of outlet flow occurs in the n=1 sub-channel extending along the inner sidewall of the elbow.
As seen from the foregoing description, although the discharge elbow provided with guide vanes of the patent document No. 1 enables the outlet of uniform parallel flows from sub-channels except n=1 sub-channel by means of providing the elbow with right angled curved guide vanes to divide the internal space of the elbow into a plurality of sub-channels similar to one another, thereby making the high-speed fluid flowing along the concave front surfaces of the guide vanes attract the separation vortices generated along the convex rear surfaces of the guide vanes to change each of the separation vortices into a fixed single vortex respectively, it has a problem in that the n=1 sub-channel experiences absence of outlet flow because of the survival of the separation vortex.